The present invention relates to a pivot assembly used as the bearing of a swing arm system actuator in a hard disk drive, and more particularly to technology that controls the generation of out gas and, in addition, simplifies the work that applies a pre-load to a ball bearing.
To illustrate an example of the present invention, ball bearings are fixed to both end parts of a shaft having a flange on one end part, such that spacing of both of these ball bearings is held by a spacer or sleeve, where a seal member is fixed on the outside of the other end of the shaft. Here, the seal member is included so that the gas and dirt generated from the grease and the like provided to the ball bearings will not be discharged. Thus, in response to this problem, conventional pivot assemblies used a seal member that was fixed to the shaft by bonding.
However, even with this type of arrangement there was the problem that gas was discharged from the bonding agent that fixed the seal member to the shaft and brought about a harmful effect on the surface of the hard disk and magnetic head. In order to solve this kind of out gas problem, pressing and fixing a seal member onto a shaft was also carried out. However, with fixing by means of pressing in, control of the allowance for pressing in was difficult and there was a lack of reliability of the fixing of the seal member. Furthermore, even after the actions of pressing in, bonding and reliably fixing a seal member to a shaft the problem of out gas from the bonding agent still remained.
Furthermore, in the conventional pivot assembly the ball bearing, shaft and sleeve were fixed by means of a bonding agent. In this case, before all the inner rings and outer rings were completely bonded, a pre-load was applied to the ball bearings. In order to obtain this pre-load, a pivot assembly was attached to a jig, and by means of the spring strength of the jig or the weight of a weight, the inner ring of the ball bearing of one side was pressed to the side of the other ball bearing, and was applied so as to eliminate the axial internal clearance that existed between the inner and outer rings and balls. For this reason, at the inner ring of the ball bearing of the side that had been pressed, that bonding agent was in an unhardened state so as to be able to move in the axial direction. Finally, the pivot assembly was heated in a heating furnace in the state in which a pre-load has been given to a ball bearing by a jig, and the unhardened state bonding agent was completely hardened.
Thus, in the conventional structure, because the pivot assembly must be carried into a heating furnace while being attached to a jig in order to apply the pre-load to a ball bearing, a large quantity of jigs were required, and moreover, jigs had to be made of a material that was heat resistant. For this reason, several disadvantages were observed such as, high manufacturing cost of a pivot assembly due to great expense of the jigs and great amount of work in the attachment and removal of jigs to and from the pivot assemblies. Furthermore, even if a UV hardness adhesive was used as a bonding agent, only the necessity to make the jigs heat resistant was eliminated but the other problems would remain.